To improve upon the aerodynamic performance of high performance vehicles, the vehicles are designed with streamlined, aerodynamic shapes. The streamlined shape of high performance vehicles generally improves aerodynamic performance by reducing the effect of drag on the vehicle. However, at high speeds, the streamlined shape can result in stability control problems. Specifically, an increased lift force acting on the vehicle causes the vehicle to rise up on the vehicle's suspension. This imparts a sluggish feel to the operator by reducing the response of the vehicle to driver inputs.
The lift force is caused by the increased velocity of the airstream passing over the top of the vehicle than the airstream passing below the vehicle. This effect is enhanced on a vehicle having a tapered tail end, as is the case with streamlined, high performance vehicles. Additionally, as the vehicle travels at high speeds, a lift force acting on the vehicle increases. The increase in lift force results in the vehicle rising on its suspension, with the negative consequences listed above following.
To counteract the negative effects of excessive lift force, high performance vehicles are equipped with spoilers. Spoilers deflect the airstream flowing over the top of the vehicle, disrupting the lift producing flow field as well as potentially increasing the down force by directing the flow field upward.
A conventional, fixed spoiler is shown in FIGS. 1A and 1B. A high performance vehicle 10 has a fixed spoiler 14 mounted on a rear end 12 thereof. The fixed spoiler 14 includes an airfoil 16 and two legs 18. The airfoil 16 extends in a width direction of the vehicle 10 body. Each of the legs 18 are disposed toward opposing edges of the airfoil 16, with a top end of each of the legs 18 being attached to a bottom of the airfoil 16, and the bottom end of each of the legs 18 being attached to the top of the vehicle rear end 12.
A fixed spoiler solves the problem of excess lift forces acting on the vehicle 10. As air flows over the top and rear end 12 of the vehicle 10, the spoiler 14 deflects a portion of the air flow, causing the deflected air flow to travel in an upward direction. This effect thereby disrupts the local flow field, thereby reducing the lift acting on the vehicle 10. Thus, the stability performance of the vehicle 10 at high speeds is improved.
However, problems exist with the conventional fixed spoiler. Initially, fixed spoilers increase the size of the rear base drag, also known as the wake bubble, behind the vehicle. While this is useful to counteract excess lift forces at high speeds, the increased size of the wake bubble is a major cause of drag on the vehicle. Thus, while effective and useful at higher speeds, the fixed spoiler impairs the performance of the vehicle at lower speeds. Further, a spoiler on the rear end of a vehicle may detract from the aesthetic appearance of the vehicle exterior.
To counteract the problems associated with conventional fixed spoilers, a deployable/retractable spoiler 20 (hereinafter, “deployable spoiler 20”) has been adopted. With reference to FIGS. 2A and 2B, the deployable spoiler 20 is shown disposed on a vehicle rear end 12, in the same general position as the fixed spoiler 14 shown in FIGS. 1A and 1B. The deployable spoiler 20 includes an airfoil 22, two legs 24, and a motor 26. The airfoil 22 is connected to the vehicle rear end 12 and the motor 26 through the two legs 24. The legs 24 are mounted on opposing sides of a bottom surface of the airfoil 22. Each of the legs 24, along bottom portions, also engage the motor 26. Through this engagement, the motor 26 can raise and lower the legs 24, thereby raising and lowering the airfoil 22. Further, the motor 26 is connected to a controller (not shown) that controls the operation of the motor 26. FIG. 2A shows the deployable spoiler 20 in a deployed condition, where the motor 26 has elevated the airfoil 22. FIG. 2B shows the deployable spoiler 20 in a retracted condition, where the motor 26 has lowered the airfoil 22.
With further reference to FIG. 2B, it is noted that when the airfoil 22 is lowered, it is shaped so as to fit within an indentation 28 formed in the rear end 12 of the vehicle 10. The vehicle rear end 12, the indentation 28, and the airfoil 22 are shaped so that when the airfoil 22 is in the retracted position, as shown in FIG. 2B, a top surface of the airfoil 22 is flush with the vehicle rear end 12. Accordingly, the vehicle rear end 12 does not appear to have a spoiler disposed thereon or therein.
In operation, the controller directs the motor 26 to either deploy or retract the airfoil 22 according to a detected speed of the vehicle 10. When the vehicle 10 is stopped or moving at lower speeds, the deployable spoiler 20 is held in the retracted, lowered position shown in FIG. 2B. When the vehicle 10 achieves higher speeds, the controller signals the motor 26 to deploy the airfoil 22. By only deploying the spoiler 20 when excess lift forces are acting on the vehicle 10, the wake bubble is not increased through the presence of a spoiler at lower speeds. Therefore, the problem of the spoiler interfering with the air flow around the vehicle at lower speeds is solved. Further, since the spoiler only deploys at higher speeds, and the spoiler is held within the indentation 28 of the vehicle rear end 12 at all other times, the aesthetic of the vehicle 10 is not altered by the spoiler while the vehicle is stopped or is travelling at lower speeds.
While the deployable spoiler addresses the problems associated with the fixed spoiler, new problems are presented by the deployable spoiler. Initially, the deployable spoiler requires several moving parts. As the number of moving parts increases, the likelihood of a failure increases. Further, the introduction of the motor and other additional parts increases the weight of the deployable spoiler relative to the fixed spoiler. Thus, some of the efficiency gains achieved by retracting the spoiler during travel at low speeds are negated by the increased vehicle weight. Finally, the cost of the deployable spoiler, due to the increase in design complexity, is greater than the cost of a fixed spoiler.
For these reasons, there exists a need for an apparatus and method to counteract the destabilizing effects of lift on a vehicle traveling at high speeds, while eliminating the problems associated with the conventional fixed and deployable spoilers.